[XFS] Replace __inline with inline

Remove the remaining uses of __inline in the XFS code base.

SGI-PV: 976035
SGI-Modid: xfs-linux-melb:xfs-kern:30774a

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>